Prosecutors handed down formal charges against Balfour on Tuesday in the deaths of Hudson's mother, brother and 7-year-old nephew, Cook County state's attorney's office spokeswoman Tandra Simonton said. Balfour was charged with three counts of first-degree murder and one count of home invasion.

At a 3 p.m. news conference, police confirmed that Balfour's ex-girlfriend cooperated in the investigation, but they would not provide further details. They also said a weapon recovered has been linked back to the homicides through casings found at the scene, and they have additional physical evidence they believe links Balfour to the killings. The shootings appear to have been a domestic-related crime between Balfour and his ex-wife, Hudson's sister Julia, police said.

"I'm confident that the evidence is there, and I'm confident that we will be successful (in prosecuting Balfour)," Chicago police Superintendent Jody Weis said at the news conference.

Balfour had been in custody on a parole violation since the bodies of Hudson's mother, Darnell Hudson Donerson, and brother, Jason Hudson, were discovered in their home Oct. 24.

Seven-year-old Julian King's body was found in a sport utility vehicle three days later.

All three had been shot to death.

Police took Balfour into custody the same day the adults' bodies were found. After 48 hours he was taken to prison on a parole violation. Police arrested him on a warrant in the deaths Monday.